What is the amount concentration of cobalt II sulfate in a solution where 100.0mL is reacted with excess of a sodium carbonate solution

Question

What is the amount concentration of cobalt II sulfate in a solution where 100.0mL is reacted with excess of a sodium carbonate solution and the following evidence is collected. Mass of filter paper =1.04g, mass of filter paper and dry precipitate = 8.98g.

Answer 1

Write the balanced equation:

CoSO₄(aq) + Na₂CO₃(aq) ==> CoCO₃(s) + Na₂SO₄(aq)

mass of precipitate (CoCO₃) = 8.98g - 1.04 g = 7.94 g

moles of CoCO₃ = 7.94 g x 1 mole/119 g = 0.0667 moles 

moles of CoSO₄ = 0.0667 moles since balanced equation shows a mole ratio of 1:1 for CoSO₄ : CoCO₃

Concentration of CoSO4 = 0.0667 moles/0.1000 L = 0.667 M (to 3 significant figures)